The sensitivity of the radioimmunoassay for hTSH has been enhanced so that the lower limit of the assay is 0.25 micron U/ml and the normal range is 1.67 plus or minus 0.68 micron U/ml. This improvement has allowed the unit to make observations not previously possible, such as precise measurements of the metabolic clearance and production rates of hTSH in man. Sensitive and specific (beta-TSH) assays have been developed for the subunits of hTSH. The aim is to study: (1) the metabolic clearance rate and production rate of the subunits of hTSH in man; (2) the controlling factors of the production and secretion of the subunits of hTSH, and (3) the use of the alpha assay as a marker for the detection of pituitary tumors. A specific and sensitive radioimmunoassay for rat TSH has been developed. The goal of these studies continues to be the development of an animal model for the clinically well known sex differences in thyroid function. In addition we plan to establish sensitive and specific radioimmunoassays for the subunits of rat TSH to follow-up on and to expand on the human subunit studies.